Machines have been in existence for some years for restringing or original stringing of tennis racquets. Tennis racquets are normally strung with strings made from materials such as nylon, gut or the like. Main strings are placed longitudinally of the head and cross strings transversely of the head to provide the surface for contact with the tennis ball. A quality tennis racquet is usually unstrung at the time of sale and can then be strung to the custom desires of the purchaser, or in general, with good strings for the normal amateur.
Under normal circumstances, the tennis racquet would be strung both as to the main strings extending along the axial length of the head and the cross strings extending perpendicularly to the main strings, in a tension range of 55 to 60 pounds of pull. In this range of pull, however, substantial differences exist as to the overall effect.
A tennis racquet has a total of 38 strings and each pound of variation is amplified by a factor of 38. Hence in a five pound range an overall difference of approximately 190 pounds results. In the professional ranks, a difference between 52 and 551/2 pounds of string tension, for example, is significant to the result that the game of a particular professional could be adversely affected by the difference. It is thus extremely important to string a tennis racquet at a proper tension.
Tennis racquet stringing machines presently in use are capable of being preset to achieve a predetermined tension on the strings as they are being strung in the racquet. Experience has proved, however, that the stringing machines are generally inaccurate and that the pounds of pull registered on an indicator for setting the machine may be off in either direction. One stringing a racquet at 55 pounds, for example, may achieve 54 or 56 pounds. In this vein, numerous complaints have been lodged where racquets strung on the same machine at a particular pound pull have seemed too tight to certain individuals and too loose to others. Such a problem presents several areas of consternation. For example, an individual having a racquet strung does not, in fact, know what tension to order when a racquet purportedly strung at 55 pounds tension, in fact is strung at 56 or 54 pounds tension. The individual is thus discontent and unsure as to the correct tension necessary to achieve his particular goal.
The calibration device of the present invention now affords an opportunity to quickly and economically calibrate each tennis racquet stringing machine. One may now properly string a racquet at a known string tension which is consistent with the desires of the user of the racquet. This capability is particularly important to a tennis professional traveling on the tennis circuit where numerous racquets will be strung at many different times and locations. A 55 pound string tension on the stringing machine at the pro's home may be exactly to his liking. A further stringing machine, however, out on the circuit may indicate 55 pound tension, while at the same time, string the racquet at a 56 pound tension. This tension inaccuracy could throw off the game of the professional significantly, to the point where a sub-par performance is given to the financial and pride detriments of the professional. The device of the present invention now permits each machine to be calibrated before stringing each racquet whereby the exact pound pull requested will always be provided.
No prior art is known that would anticipate or suggest the present invention.